1. Field of the Invention
The present invention relates to a fuel supply amount control system suitably adapted for starting various types of engines such as a V-type, eight-cylinder, four-cycle engine mounted on a boat propulsion unit in an outboard motor or an inboard-outboard motor, and also relates to a boat propulsion unit including the fuel supply amount control system.
2. Description of the Related Art
Conventionally, separate fuel injection patterns are used before and after a cylinder stroke determination (cylinder identification) for improving engine startability when an engine is started.
That is, before the cylinder stroke determination, it is not determined which stroke the cylinder is in among an intake, compression, expansion (combustion), and exhaust stroke. Therefore, fuel is injected into each cylinder at once immediately after crank starting by rotation of a starter motor in order to supply fuel for ignition and combustion. As an example, FIG. 5 shows an engine constructed such that a crank angle is divided into 36 equal portions of 10 degrees each. Each of the first through thirty-fourth portions has a detected tooth and the thirty-fifth and thirty-sixth portions have no tooth. When a crankshaft sensor signal is at portion 7, each injector on the first through eighth cylinders is driven at once to inject fuel.
On the other hand, after the cylinder stroke determination, since it is already determined which stroke the cylinder is in among an intake, compression, expansion (combustion), and exhaust stroke, each cylinder can be injected with fuel at the optimum timing. As such an example, FIG. 6 shows cylinder groups in the above described engine, which are the first and sixth cylinders, the eighth and fifth cylinders, the fourth and seventh cylinders, and the third and second cylinders. Fuel is injected into each group by driving each injector during the compression and exhaust strokes.
Regardless of before or after the cylinder stroke determination, the same arithmetic expression is used to determine the fuel amount during a period from the start of cranking to completing the engine startup (see, for example, paragraphs [0019] and [0020] of JP-A-2004-197700).
However, since which stroke each cylinder is in among an intake, compression, expansion (combustion), and exhaust stroke, is determined by the cylinder stroke determination for the first time, it is considered that the required fuel supply amounts are inherently different between before and after the cylinder stroke determination to achieve engine startup in the shortest time. Nevertheless, since the fuel supply amount (for example, injection pulse width W1 before the cylinder stroke determination shown in FIG. 5 and injection pulse width W2 after the cylinder stroke determination shown in FIG. 6) has been the same before and after the cylinder stroke determination, the fuel supply amount is not always optimum before and after the cylinder stroke determination. Accordingly, engine startup in the shortest time is not achieved.